The relationship between the structure and function of molecules is a fundamental issue in the study of biological and other chemistry-based systems. Structure-function relationships are important in understanding, for example, the functions of enzymes, cellular communication, and cellular control and feedback mechanisms. Certain macromolecules are known to interact with and bind to other molecules having a specific three-dimensional spatial and electronic distribution. Any macromolecule having such specificity can be considered a receptor, whether the macromolecule is an enzyme, a protein, a glycoprotein, an antibody, an oligonucleotide sequence of DNA, RNA, or the like. The various molecules to which receptors bind are known as ligands.
Pharmaceutical drug discovery is one type of research that relies on the study of structure-function relationships. Much contemporary drug discovery involves the discovery of ligands with desirable patterns of specificity for biologically important receptors. Thus, the time necessary to bring new drugs to market could be greatly reduced through the use of methods and apparatus that allow rapid generation and screening of large numbers of ligands.
A common way to generate such ligands is to synthesize libraries of ligands on solid phase resins. Techniques for solid phase synthesis of peptides are described, for example, in Atherton and Sheppard, Solid Phase Peptide Synthesis: A Practical Approach, IRL Press at Oxford University Press, Oxford, England, 1989. Techniques for solid phase synthesis of oligonucleotides are described in, for example, Gait, Oligonucleotide Synthesis: A Practical Approach, IRL Press at Oxford University Press, Oxford, England, 1984. Both of these references are incorporated herein by reference.
Since the introduction of solid phase synthesis methods for peptides, oligonucleotides and other polynucleotides, new methods employing solid phase strategies have been developed that are capable of generating thousands, and in some cases even millions, of individual peptide or nucleic acid polymers using automated or manual techniques. These synthesis strategies, which generate families or libraries of compounds, are generally referred to as "combinatorial chemistry" or "combinatorial synthesis" strategies.
To aid in the generation of combinatorial chemical libraries, scientific instruments have been produced that automatically perform many or all of the steps required to generate such libraries. An example of an automated combinatorial chemical library synthesizer is the Model 396 MPS fully automated multiple peptide synthesizer, manufactured by Advanced ChemTech, Inc. ("ACT") of Louisville, Ky.
The Model 396 MPS is capable of generating up to 96 different peptides (or other small molecules) in a single run. The syntheses occur simultaneously, with one amino acid being added to each growing polypeptide chain before addition of the next successive amino acid to any polypeptide chain. Thus, each growing polypeptide chain contains the same number of amino acid residues at the end of each synthesis cycle. The syntheses occur in an ACT proprietary plastic reaction block that has 96 reaction chambers.
Although the ACT Model 396 works for its intended purpose, it possesses several shortcomings. For example, since the ACT reaction blocks are machined from a single piece of plastic, they require extremely intricate machining and are quite expensive to manufacture. Moreover, should a portion of a block become damaged or contaminated in some way, the entire reaction block would have to be discarded; there is no way to replace individual portions of an ACT block. An additional drawback of the plastic ACT reaction blocks is that they cannot be efficiently heated or cooled to aid in chemical reactions that may require such heating or cooling.
Certain processes and chemistries require that the chemical reagents (which may be reactants, solvents, or reactants dissolved in solvents) be kept under an inert or anhydrous atmosphere to prevent reactive groups from reacting with molecular oxygen, water vapor, or other agents commonly found in air. Examples of atmosphere or moisture sensitive chemistries include peptide chemistry, nucleic acid chemistry, organometallic, heterocyclic, and other chemistries commonly used to construct combinatorial chemical libraries.
Although the ACT reaction block can maintain an inert atmosphere when locked in place on the work station of the Model 396 MPS, there is no way to maintain an inert atmosphere once an ACT reaction block is removed from the work station. Thus, the reaction block must remain docked at the work station during the entire synthesis cycle. Since many reactants require several hours to react, this represents significant down time for the Model 396 MPS, as it remains idle during the reaction period.
The ACT reaction block includes 96 reaction chambers; however, the compounds generated in the ACT reaction block cannot be transferred directly into a standard 96-well microtiter plate because the distance between the outlets of the reaction chambers is too great. When reactions are complete, the user must transfer the contents of the reaction chambers into an array of 96 flat bottom glass vials supported in a plastic frame. The user must then manually pipette fluid from the glass vials into a microtiter plate for further analysis.
U.S. Pat. Nos. 3,944,188 and 4,054,141 to Parker et al. disclose a concentrating vortexing shaker that can receive a thermally conductive vessel block. The vessel block of Parker et al. has a plurality of openings for receiving sample laboratory vessels; the vessel block also has passages through which a hearing or cooling liquid may be passed. After the vessel block of Parker et al. is mounted on the vortexing shaker, an air-tight cover may be attached to the block, forming a chamber over the vessels in the block. A vacuum may then be applied to the chamber.
Although the vortexing shaker and vessel block of Parker et al. may be useful to facilitate particular types of chemical reactions (and when only a small number of samples needs to be generated), the structures disclosed in Parker et al. possess many disadvantages that make them unsuitable for use in the efficient generation of chemical libraries. For example, a vacuum or inert atmosphere may be maintained in the vessel block of Parker et al. only when the vessel block is mounted on the vortexing shaker. Moreover, nothing can be added to the vessels of Parker et al. when the air-tight cover is attached to the vessel block.
To secure the vessel block of Parker et al. to the vortexing shaker, vacuum and cooling hoses from the vortexing shaker must be attached to the block manually, and the block itself must be secured to the shaker with a manually operated knob. Again, a common objective of combinatorial synthesis is to generate a very large number of compounds. The several manual operations required to use the vessel block and vortexing shaker of Parker et al. therefore make the use of these structures too inefficient and time consuming for use in the generation of very large chemical libraries.
In light of the deficiencies in the prior art, there remains a need in the art for an apparatus that allows for the fully automated and rapid generation of combinatorial chemical libraries.